1. Field of the Invention
The present invention relates to a magnetic field device for generating an extremely highly uniform magnetic field, and more particularly to a uniform magnetic field device particularly adapted to obtain a high resolution power in a nuclear magnetic resonance device.
2. Description of the Prior Art
As it is considered that the present invention can be readily understood by explaining the case where the present invention is applied to a nuclear magnetic resonance analyzer, for example, a principle of the nuclear magnetic resonance analyzer will be first explained briefly in conjunction with FIG. 1. A material sample 12 to be analyzed is placed between a pair of magnets 1a and 1b which establish an extremely strong and uniform, unidirectional polarized magnetic field. Applied further to the material sample 12 is a radio-frequency magnetic field generated by a radio-frequency oscillator 13 and a radio-frequency coil 14, which radio-frequency magnetic field is applied normally to the unidirectional, polarized magnetic field so that through a precise and proper combination of those two magnetic fields, the nuclei of the sample are caused to produce magnetic resonance absorption to generate an electric signal, which is then detected and displayed by a detection-display device 15. In this manner, molecule structure of the material sample or the like can be analyzed.
Furthermore, a great deal of information, both qualitative and quantative, for the chemical and physical properties of the sample under study can be derived from the magnetic resonance absorption signal. As technology advances, a requirement of higher resolution power occurs. To accomplish such a high resolution power, it is important that the sample is placed in a uniform strength magnetic field. Thus, many efforts have been made with various devices to obtain a uniform magnetic field. In general, great attention has been paid to a winding of a strong electromagnet for generating a magnetic field, provision of magnet poles of the material and proper alignment of the magnet poles on a coil structure.
For example, a space field gap required in the magnetic resonance analyzer is in the order of 10 mm but a variation rate of a space magnetic field distribution at a magnetic field strength of several thousands oersteds (Oe) or more should be less than 0.01%. In the past, as a polarized magnetic field generator of this type, as shown in FIG. 2, a parallel gap 3 defined by magnets 1a and 1b and magnetically homogenized pole pieces 2a and 2b has been used to generate a space magnetic field between the parallel gap 3. However, from a standpoint of obtaining a highly uniform magnetic field, it has a drawback in that larger magnets are required relative to magneto-motive force required when the parallel gap is used. Furthermore, there exists a difficulty in strictly tailoring the parallelism of the gap in order to generate a uniform magnetic field. The strength of the magnetic field required in the magnetic resonance analyzer is more than 10,000 Oe and the prior art magnets which used the parallel gap required a magnetic device which amounted to more than 2 tons in weight to attain such strength. Therefore it was a serious problem to maintain efficiently the magnetic field strength in the parallel gap. Furthermore, the generation of a uniform magnetic field in the parallel gap induced complex mechanism in the prior art magnetic resonance device and many unstable factors due to external factors such as temperature and external disturbance magnetic fields. As a result, great effort and care has had to be paid to maintenance. Even after such troublesome arrangements, the magnetic field might become nonuniform during transportation of the device or by external vibration and hence readjustment has been frequently required.